Method of processing end portions of optical fibers and optical fibers having their end portions processed

ABSTRACT

An end portion of an optical fiber element  11  is dipped into an etchant to shape that portion of the fiber element immersed in said etchant into a coaxial reduced-diameter portion by etching while causing that portion of the fiber element where the etchant rising to a certain height above the level surface of the etchant due to surface tension into a conical tapered surface portion which is formed between the reduced-diameter portion and un-etched portion of the fiber element, and subsequently thereafter, the reduced-diameter portion is cut to have a very short length thereof remained.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a method of processing end portions ofoptical fibers utilized in, for example, optical communications, andmore particularly to a method of processing end portions of opticalfiber elements which elements are well suitable for end-to-endconnecting together and also relates to such optical fibers having endportions specifically processed.

[0003] 2. Description of the Related Art

[0004]FIGS. 19 and 20 show the configuration of the end portion of anoptical fiber to be connected to a conventional optical connector. Inthe drawings, the reference numeral 10 indicates the optical fiber and20 the ferrule bonded to the end portion of the optical fiber 10. Theferrule 20 is of a hollow cylindrical shape and has a through-bore 21formed through its center axis for receiving an optical fiber element 11which is a bare fiber exposed by removing away a protective coatingtherefrom. The fiber element 11 is inserted into the through-bore 21 andfixed or adhered thereto by adhesive 20A.

[0005] In a conventional optical connector, the end terminal face of theferrule 20 having an optical fiber element 11 adhesively fixed theretois ground to a convex spherical shape, and a pair of such identicalferrules 20 thus shaped are then brought into end-to-end abutment andjoined together within a split sleeve 30 (see FIG. 21). For thisprocess, the PC (Physical Contact) joining method is used which involvesapplying urging pressure to the end faces of the pair ferrules 20 byresilient springs (not shown) to elastically deform the core of therespective optical fiber elements 11 of the optical fibers 10 lying atthe apices of the convex spherical ends. With this PC joining method, noair space is produced between the optical fiber elements 11, allowingfor the joining at a low transmission loss.

[0006] Currently, however, optical connectors configured so as toconnect optical fiber elements 11 directly together without the use ofthe ferrules 20 have been designed in view of the demand for morecompactness and finer pitches of optical connectors. But, the opticalconnector of such configuration still requires the PC joining method inorder to accomplish the purpose of reducing the loss. Further, theurging pressure for effecting the PC joining in this type of opticalconnector is characterized in that it is generated by axiallycompression-deforming the optical fiber elements 11 and utilizing therestoring force (which will be hereinafter referred to as buckling load)from the compressive deformation.

[0007] In this regard, the magnitude of the buckling load generated bycompression-deforming the optical fiber elements 11 is on the order of0.2-0.4N. Depending on the condition of the end face of the opticalfiber, particularly if the end face has been cut at an angle θ which isnot a right angle with respect to the fiber axis as illustrated in FIG.22A, even a buckling load TH exerted on such fiber as shown in FIG. 22Bmay fail to sufficiently compression-deform the opposed cores, resultingin occurrence of a gap G between the opposed fiber ends as shown in FIG.22C and hence inability to accomplish the PC connection. Consequently,it is undesirably difficult to achieve stable optical properties.

[0008] One approach currently proposed to solve this difficulty is toform the end portion of an optical fiber in a shape of a convergenttaper by using the technique as disclosed in the Japanese PatentPublication Kokoku 3-50246, and then cut the tapered end to obtain aflat end face, thereby to optically couple a pair of the thus obtainedoptical fibers together by butt-joining the flat end faces.

[0009] This method allows for facilitating the deformation of theopposed fibers at their extreme cut ends to secure good optical couplingresult even if the end faces are cut more or less at an angle θ, becausethe end faces to be abutted together are reduced in area due to theconvergent taper.

[0010] Nevertheless, the thus obtained optical fiber elements 11 have adrawback that the optical fiber elements 11 are vulnerable to failuredue to their reduced mechanical strength when they are subjected to theconnecting method as mentioned above by abutting them against each otherand subjecting them to buckling load.

[0011] In order to overcome this drawback, there was an approach towardproviding the peripheral surface of the optical fiber element 11 with acoating film 11C of carbon, resinous material or the like as illustratedin FIG. 23.

[0012] However, when an attempt is made to form a taper end portion atits terminal end of such optical fiber element 11 covered with thecoating film 11C, by using the etching technique in accordance with themethod as disclosed in the Japanese Patent Publication Kokoku 3-50246,the etching process would start with the end face of the optical fiberelement 11 which is only the portion exposed from the coating film 11Cwith the peripheral surface of the cladding 11B of the optical fiberelement 11 being covered with the coating film 11C, so that the etchingwould proceed from the core 11A located in the center of the fiberelement 11, with the result that the optical fiber element 11 would beetched in a generally cylindrical form, and thus end in failure to formtapered surface portions.

[0013] For this reason, the present inventors endeavored to solve thisdrawback in the technique of forming a taper on an optical fiber element11 coated with a coating film 11C, and conceived such a technique as todeposit a resist film 13 on the end terminal surface of the opticalfiber element so as to cover the entire end face of the core 11A and theradially inner half part of the cylindrical end face of the clad 11B asshown in FIG. 24 prior to effecting the etching process and then dippingthe end portion of the fiber element thus covered with the resist film13 into an etching solution J as shown in FIG. 25.

[0014] According to this endeavored method, since the end face of thecore 11A is fully protected from the etching by the resist film 13, itwas found that the immersed end portion of the fiber element is formedwith a reduced-diameter portion 14 extending upward from its extremeend.

[0015] It was also found that the fiber element was provided with atapered surface portion TP at the upper part of the reduced-diameterportion, that is, a part of the fiber element corresponding toultimately at an elevated portion from the liquid level of the etchantJ.

[0016] After a desired tapered surface portion TP has been obtained,those portions of the coating film 11C corresponding to thereduced-diameter portion 14 and the tapered surface portion TP areremoved.

[0017] However, this endeavored method still has the disadvantage thatit requires an additional step of applying a resist film 13 to the endface of an optical fiber element 11 prior to forming a tapered surfaceportion thereon, and also another additional step of removing thecoating film. It makes thus the manufacturing process correspondinglycumbersome. Particularly in the case of an optical fiber having amultiplicity of optical fiber elements 11 integrally incorporatedtherein such as the flat tape type optical fiber, the operation ofdepositing a resist film 13 to the end face of each individual opticalfiber element 11 has proved too cumbersome to put this method intopractical use.

[0018] Turning now back to the prior art of Japanese Patent PublicationKokoku 3-50246, when the optical fiber element is cut directly on thetapered surface portion as disclosed this prior art, the cutter edge mayslip axially along the angular tapered surface portion to exert an axialforce on the fiber element during the cutting process. Consequently,this method has another drawback that flaws such as cracks may possiblyoccur in the cut portions.

[0019] In addition, in order to form tapered surface portions on theindividual fiber elements 11 of a tape type optical fiber array 10Tcomprising a plurality of optical fiber elements 11 held by a tape-likesport 12T as illustrated in FIG. 26, the Japanese Patent PublicationKokoku 3-50246 also discloses a method involving dipping the individualfiber elements 11 in an etchant J. As one example, it is disclosed thateven if the fiber elements immersed in the liquid are not equal inlength, a plurality of tapered surface portions which are shaped inconical terminal ends are uniformly formed in their lengths, since thoseportions of the fiber elements immersed in the liquid should becompletely dissolved by dipping them for a sufficiently longer period oftime (such as, 30-60 minutes) which is enough for the complete dissolve.

[0020] The present inventors have discovered, however, when theabove-identified prior art technique were applied to a tape type opticalfiber array 10T comprising a multiplicity of individual fiber elements11 having as fine an array pitch PN as around 0.25 mm so as toaccomplish the purpose of the present invention, a specific phenomenonoccurred that the levels of the respective liquid heads of the etchantwhich heads are adhering to the respective associated fiber elements,could rise higher as it is closer to the middle of the array due to thesurface tensions acting on the respective liquid heads adhering toindividual fiber elements 11 overlapping to each other (see FIG. 27).

[0021] As a result, the troubles occur that the axial dimension (length)L of the tapered surface portion TP formed by etching gets successivelylonger in the order of L1<L2<L3<L4 toward the middle of the array of thefiber elements 11 and that the positions of the tapered surface portionsare displaced with respect to each other. Especially, the axialdimensions L1<L2<L3<L4 of the tapered surface portions TP tend to belonger than that obtained when the etching is conducted on a singlefiber.

[0022] By way of example, if the array pitch PN of the fiber elements 11is 0.25 mm and the diameter of the fiber elements 11 is 0.125 mm (125μm), the axial dimensions L1<L2<L3<L4 of the tapered surface portions TPwill be around 0.3 to 0.5 mm. On the other hand, when the etching isconducted on a single fiber, the axial dimension of the tapered surfaceportion TP will be around 0.1 mm. This means that the axial dimension Lof the tapered surface portion TP formed on the multiple-fiber typeoptical fiber array will be about 3 to 5 times as long as that of thesingle-core fiber.

[0023] As the axial dimension L of the tapered surface portion TPincreases, the strength of the tapered surface portion TP adjacent itsforward end correspondingly decreases. With repeated connectingoperations of optical connectors, fatigue is built up in the taperedsurface portion TP, causing a durability problem.

[0024] As discussed above, the conventional methods and the priorattempt conducted by the present inventors are still insufficient due tovarious problems. Accordingly, there has been a need for obtaining aneffective and practical method for processing end portions of opticalfibers as well as optical fiber having an improved end portion which isapplicable to the repeated connection purpose.

SUMMARY OF THE INVENTION

[0025] A first object of this invention is to provide an optical fiberelement having a tapered surface portion adjacent to its end and areduced-diameter end portion extending forwardly from the taperedsurface portion and also to provide an optical fiber end portionprocessing method for forming a tapered surface portion having areduced-diameter end portion extending forwardly therefrom.

[0026] This reduced-diameter end portion extended from the taperedsurface portion is adapted to be butt-joined to the identicalreduced-diameter end portion of another identical opponent optical fiberelement.

[0027] A second object of this invention is to provide an optical fiberend portion processing method capable of forming a tapered surfaceportion having a reduced-diameter end portion extending therefrom on ancoated optical fiber element as well by simple steps.

[0028] A third object of this invention is to provide an optical fiberend portion processing method capable of forming tapered surfaceportions with reduced-diameter end portions on a plurality of paralleljuxtaposed optical fiber elements forming an optical fiber arraytherewith. These tapered surface portions of the respective opticalfiber elements have approximately equal reduced axial dimensions orlengths which are also same as that obtained by etching of a singleoptical fiber element, to thereby provide the tapered surface portionwith an enhanced durability.

[0029] In order to accomplish the first object, this invention providesan optical fiber end portion processing method wherein: an optical fiberelement having a core in the axial center thereof and a cylindricallyformed clad surrounding the periphery of the core is dipped at an endportion thereof into an etchant while holding the element in an attitudesubstantially perpendicular to the surface of the etchant; the portionof the fiber element dipped below the liquid level of the etchant isshaped into a reduced-diameter portion by etching in the etchant whilethe portion of the etchant is caused to rise along outer periphery ofthe clad of the fiber element to a certain height M (see FIG. 1) abovethe liquid level of the etchant due to surface tension to thereby shapethe portion of the fiber element contacted by said rising portion of theetchant into a tapered surface portion extending from thereduced-diameter portion up to the outer diameter of the non-etchedportion of the clad; the period of time for the etching process isspecially controlled so that the etching process is terminated whenevera desired tapered surface portion is obtained, at the moment oftermination of the etching process, the reduced-diameter portion 14 of adesired diameter which is slightly larger than that of the core isformed in conjunction with the tapered surface portion; and then thereduced-diameter portion 14 is cut at a point spaced by a very shortdistance from the boundary between the tapered surface portion and thereduced-diameter portion toward the reduced-diameter portion so as toleave a reduced-diameter end portion 14T continuously joining to thetapered surface portion.

[0030] The reduced-diameter end portion has to have axial length m whichis desired not to exceed to its own diameter.

[0031] In order to accomplish the second object, this invention providesan optical fiber end portion processing method wherein: an optical fiberelement having a core in the axial center thereof, a cylindricallyformed clad surrounding the periphery of the core and a coating filmformed around the peripheral surface of the clad is shaped to have aresidual coating film in a certain distance from the extreme end of theoptical fiber element and a coating film-removed section of a certainlength A (see FIG. 3) from which the coating film is removed in aposition adjacent to the residual coating; the thus shaped optical fiberelement at the entire part of the residual coating thereof and at abouthalf of the coating film-removed section thereof is dipped into anetchant while holding the fiber element with its axis in an attitudesubstantially perpendicular to the surface of the etchant in such amanner that the top half part of the coating film-removed section ispositioned upwardly away from the liquid level of the etchant; shapingthat the lower half part of the exposed clad at the coating film-removedsection of the fiber element immersed in the etchant is shaped into areduced-diameter portion by etching in the etchant while the portion ofthe etchant is caused to rise along outer periphery of the clad of thefiber element to a certain height M above the liquid level of theetchant due to surface tension to shape the outer periphery of the cladin a length of M above the liquid level contacted by said rising portionof the etchant into a tapered surface portion extending from thereduced-diameter portion up to the outer diameter of the non-etchedportion of the clad; the etching process is terminated whenever adesired tapered surface portion together with a desired reduced-diameterportion 14 is obtained; and then the reduced-diameter portion 14 is cutat a point spaced by a very short distance from the boundary between thetapered surface portion and the reduced-diameter portion toward thereduced-diameter portion so as to leave a reduced-diameter end portion14T continuously joining to the tapered surface portion, thereduced-diameter end portion having a very short length corresponding tothe very short distance.

[0032] In order to accomplish the third object, this invention providesan optical fiber end portion processing method wherein a levelcontrolling means for restraining the liquid level of the etchant isprovided upward from the liquid level in such a manner that the lowerend thereof contacts to the liquid surface of the etchant whereby theaxial dimension of the tapered surface portion formed on the opticalfiber element is controlled at a desired value.

[0033] This invention also provides the optical fiber end portionprocessing method wherein the level controlling means is constituted byan etching-resistant film formed around the peripheral surface of theoptical fiber element.

[0034] This invention further provides the optical fiber end portionprocessing method wherein the level controlling means is constituted bya coating film applied to the optical fiber element.

[0035] This invention further provides the optical fiber end portionprocessing method wherein the level controlling means comprises a flatplate made of etching-resistant material with through-apertures formedthrough the flat plate perpendicularly to the plane of the flat plate,each of the through-apertures having a diameter slightly larger than theouter diameter of the corresponding optical fiber element.

[0036] This invention further provides the optical fiber end portionprocessing method wherein a liquid having a specific gravity lower thanthat of the etchant is added to the etchant.

[0037] This invention further provides the optical fiber end portionprocessing method wherein a plurality of optical fiber elements are heldin parallel to each other to form a fiber array therewith by using asingle common covering or supporting member.

[0038] Still further, this invention provides an optical fibercomprising an optical fiber element having a tapered surface portionformed adjacent to its end part with a reduced-diameter end portion 14Tformed integrally with the forward end of the tapered surface portion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1 is a cross-sectional view illustrating a first embodimentof the optical fiber end portion processing method according to thisinvention;

[0040]FIG. 2 is a side view illustrating the construction of the forwardend portion of the optical fiber element obtained by the embodimentshown in FIG. 1;

[0041]FIG. 3 is a cross-sectional view illustrating a second embodimentof the optical fiber end portion processing method according to thisinvention;

[0042]FIG. 4 is a side view illustrating the configuration of theoptical fiber element obtained by the embodiment shown in FIG. 3;

[0043]FIG. 5 is a side view illustrating the optical fiber element shownin FIG. 4 having the reduced-diameter end portion 14T of a length mafter the rest of the reduced-diameter portion 14 has been removed;

[0044]FIG. 6 is a cross-sectional view illustrating a third embodimentof the optical fiber end processing method according to this invention;

[0045]FIG. 7 is a side view illustrating the configuration of theoptical fiber element obtained by the method shown in FIG. 6;

[0046]FIG. 8 is a side view illustrating the optical fiber element shownin FIG. 7 after the reduced-diameter portion has been removed;

[0047]FIG. 9 is an enlarged, cross-sectional view illustrating theprincipal parts of the optical fiber end portion processing method shownin FIG. 6;

[0048]FIG. 10 is a cross-sectional view illustrating a fourth embodimentof the optical fiber end processing method according to this invention;

[0049]FIG. 11 is a side view illustrating the configuration of theoptical fiber element obtained by the method shown in FIG. 10;

[0050]FIG. 12 is a cross-sectional view of an etching apparatusincluding a cross-section taken on line 12-12 of the liquid levelcontrolling means shown in FIG. 13, for illustrating a fifth embodimentof the optical fiber end processing method according to this invention;

[0051]FIG. 13 is a perspective view illustrating the construction of theliquid level controlling means used in the embodiment of FIG. 12;

[0052]FIG. 14 is a side view illustrating the configuration of theoptical fiber element obtained by the method shown in FIG. 12;

[0053]FIG. 15 is a cross-sectional view of an etching apparatus forillustrating a modified example of the processing method shown in FIG.12;

[0054]FIG. 16 is a cross-sectional view of an etching process forillustrating a sixth embodiment of the processing method shown in FIG.10;

[0055]FIG. 17 is a cross-sectional view of an etching process forillustrating a modified example of the processing method shown in FIG.12;

[0056]FIG. 18 is a cross-sectional view illustrating a seventhembodiment of the optical fiber end processing method according to thisinvention;

[0057]FIG. 19 is a perspective view for illustrating a prior art;

[0058]FIG. 20 is a cross-sectional view illustrating the details of theferrule shown in FIG. 19;

[0059]FIG. 21 is a cross-sectional view illustrating two of the ferruleshown in FIG. 19 being joined together;

[0060] FIGS. 22A-22C are structures illustrating the drawbacks of theprior art shown in FIGS. 19-21;

[0061]FIG. 23 is a front view illustrating the construction of anoptical fiber element provided with a coating film;

[0062]FIG. 24 is a cross-sectional view illustrating the pre-treatmenttechnique developed by the present inventors so as to form a taperedsurface portion on the optical fiber element provided with a coatingfilm as shown in FIG. 23;

[0063]FIG. 25 is a cross-sectional view illustrating the etchingtechnique developed by the present inventors so as to carry out thistechnique on the optical fiber element which has been subjected to thepre-treatment as illustrated in FIG. 24;

[0064]FIG. 26 is a side view illustrating the construction of a knowntape-type optical fiber array;

[0065]FIG. 27 is a cross-sectional view illustrating an etching processcarried on the tape-type optical fiber array to form a tapered surfaceportion thereon, which is conducted by the present inventors; and

[0066]FIG. 28 is a side view illustrating the configuration of theoptical fiber elements of the tape-type optical fiber array comprising aplurality of optical fibers gathered together in the form of a tape, asobtained by the etching process shown in FIG. 27.

DETAILED DESCRIPTION OF THE INVENTION

[0067] Various embodiments of this invention will now be described withreference to the accompanying drawings. Like numerals and charactersindicate like elements throughout the various drawings.

First Embodiment

[0068] Referring to FIGS. 1, there is shown a first embodiment of theoptical fiber end portion processing method according to this invention.The embodiment illustrated in FIGS. 1 is directed to forming a taperedsurface portion TP on an optical fiber element 11 having no coating film11C coated around the clad 11B (see FIG. 23). In this case, the clad ofan optical fiber element 11 is exposed from a covering 12 and is dippedinto an etchant J such as hydrogen fluoride, for example.

[0069] The length of the immersed portion of the optical fiber element11 (submerged below the liquid level) should be long enough as comparedto the diameter of the optical fiber element 11. By way of example, forthe optical fiber element 11 having a diameter of 0.125 mm with a corehaving a diameter of slightly shorter than 0.05 mm, the immersed lengthmay be about 12.5 mm which is one hundred times the diameter.

[0070] The optical fiber element 11 is dipped into an etchant J whileholding the element in an attitude substantially perpendicular to theliquid surface of the etchant J. If necessary, any suitable holdingmeans or member (not shown) for supporting the fiber element in itsappropriate state may be utilized. Around the peripheral surface of thatportion of the optical fiber element 11 contacted by the liquid surface,the etchant J rises in the form of a taper over a distance M due to thesurface tension and attaches to the peripheral surface of the opticalfiber element 11. By this raised etchant J attached to the peripheralsurface, the portion of the fiber element extending the distance M fromthe liquid surface is etched to be formed into a tapered surface portionTP. The portion of the optical fiber element 11 extending below thetapered surface portion TP (the portion immersed in the liquid, lower asviewed in the drawing) is formed into a reduced-diameter portion 14which has been reduced in diameter generally constantly along the lengththereof It is thus to be understood that the tapered surface portion TPis formed as a result of the diameter varying gradually from thediameter of the reduced-diameter portion 14 up to the outer diameter ofthe clad 11B.

[0071] At the time when the diameter of the reduced-diameter portion 14has reached a target value, say 50 μm, which is determined by the timelapsed after the initiation of the etching process, and which isselected to be slightly larger than the diameter of core, the etching isterminated.

[0072] In this regard, the Japanese Patent Publication Kokoku 3-50246discloses nothing about terminating the etching process in a halfway. Inother words, it merely discloses that the etching process is continueduntil the reduced-diameter portion has been completely etched out so asto obtain a conical shaped end portion.

[0073] The present invention is specifically characterized bycontrolling the length of time period for carrying the etching process,which is different from the above-identified prior art.

[0074] Subsequently, the reduced-diameter end portion 14 is severed.More specifically, according to this invention, the cutting is madeperpendicularly to the fiber axis at a point m spaced slightly,preferably 20 to 30 μm from the boundary between the tapered surfaceportion TP and the reduced-diameter portion 14 toward thereduced-diameter portion. This leaves a reduced-diameter end portion 14Twith a length m integrally joining to the tapered surface portion TP(see FIG. 2).

[0075] The adoption of such cutting point allows for severing theoptical fiber element 11 without the risk of producing any defectsthereon.

[0076] If the optical fiber element having only the tapered surfaceportion as shown in the above-identified prior art is to be cut directlyon the tapered surface portion TP, not only it would be difficult to cutit exactly at a desired position, but also the cutter edge would cut itwith a force tending to slip the edge axially along the angular taperedsurface portion. Due to such an axially acting force, some unevenness aswell as flaws such as cracks may result on the cut surfaces.

[0077] In this connection, the Japanese Patent Publication Kokoku3-50246 discloses the use of arc discharge device to cut a conical endportion of an optical fiber element since this optical fiber isapplicable to connect to optical element. This prior art also evidentlydescribes that the use of a cutter is impossible, in view of the factthat the optical fiber elements according to that patent are providedwith conical pointed ends.

[0078] In contrast, according to this invention, since thereduced-diameter end portion 14 is cut at a selected point, there occursno axial force exerted on the cutter edge during the cutting operation.As will be appreciated, this invention ensures stable cutting andprovides for reducing the incidence of flaws on the surfaces.

Second Embodiment

[0079]FIG. 3 illustrates a second embodiment directed to forming atapered surface portion TP on an optical fiber element 11 which has acoating film covering the clad. In this instance, a coating film-removedsection A is formed on an optical fiber element 11 at an arbitrarylocation away from the extreme end of the optical fiber element. Thecoating film 11C is generally made of carbon, resinous material or thelike. Such coating film 11C may be removed by irradiating laser beamwith a laser beam irradiation apparatus. The length of the coatingfilm-removed section A may be arbitrarily chosen. As a guide, it may belonger than that of the tapered surface portion TP to be formed. Thisembodiment is characterized by leaving a residual coating film 11C-1below the coating film-removed section A. With regard to the etching onthe portion of the optical fiber element corresponding to the residualcoating film 11C-1, it is to be understood that the etching will proceedin both directions, namely from the far end side of the residual coatingfilm toward the coating film-removed section A and from the inner endside of the residual coating film toward the far end side of theresidual coating film 11C-1.

[0080] On the side of the far end of the residual coating film 11C-1 theetching proceeds in a cylindrical manner from the core to the clad,whereas on the side of the coating film-removed section A of theresidual coating film 11C-1 the etching proceeds in a sense to thin theclad layer.

[0081] The etching tending to thin the clad layer progresses downwardlyas shown in FIG. 3 until it meets the cylindrical etching progressingupwardly from the far end of the residual coating film 11C-1, whereuponthe diminished residual coating film 11C-1 is separated from the opticalfiber element 11 and sinks in the etchant J.

[0082] When the etching initiated from the far end side which is toshape the optical fiber element 11 in a cylindrical form encounters theetching initiated from the coating film-removed section A side, thecylindrical portion formed on the far end side is rapidly extinguished,so that the optical fiber element will ultimately have a substantiallyflat lower end face remaining.

[0083] As is appreciated from the forgoing, without the need fordepositing a resist film 13 as described hereinbefore with reference toFIG. 24, the optical fiber element 11 is formed with a reduced-diameterend portion 14 which is similar to that obtained in the embodiment shownin FIG. 1 and which has an ultimately flat end face. In addition, on thetop of the reduced-diameter end portion 14 a tapered surface portion TPis formed by the etchant J rising due to its surface tension, as shownin FIG. 4. Upon the time when the diameter of the reduced-diameterportion 14 has reached a predetermined value being determined, theetching is terminated. After the termination of the etching, the opticalfiber element 11 is cut so as to leave a short reduced-diameter endportion 14T, whereby an optical fiber 10 having a tapered surfaceportion TP formed with the reduced-diameter end portion at the extremeend thereof as shown in FIG. 5 is obtained.

Third Embodiment

[0084] FIGS. 6 to 9 illustrate a third embodiment which is capable ofprecisely restraining the location where a tapered surface portion TP isto be formed. This embodiment is characterized in providing the coatingfilm-removed section with a liquid level controlling means 40 fordefining the level of the etchant J. In the embodiment shown in FIG. 6,the liquid level controlling means 40 is constituted by a residualcoating film.

[0085] Specifically in this embodiment, assuming that the residualcoating film 11C-1 shown in FIG. 3 is referred to as a first residualcoating film.

[0086] This embodiment is characterized in that a second residualcoating film 11C-2 having a length M′ is disposed in a midst of thecoating film-removed section A so as to divide it into lower portion Awhich is called as a first coating film-removed section and upperportion B called as a second coating film-removed section as shown inFIG. 6.

[0087] The second residual coating film 11C-2 constitutes a liquid levelcontrolling means 40.

[0088] The etching is initiated with the lower end of the liquid levelcontrolling means 40 contacted by the liquid surface of the etchant J.(see FIG. 9)

[0089] It is required that the liquid level controlling means 40 shouldat least surround the peripheral surface of the optical fiber element 11and should have a flange-like portion protruding even slightly beyondthe surface of the clad layer 11B. The amount that the etchant J risesup due to the surface tension is thus restricted by this protrudingportion.

[0090] When the etching is initiated in this condition, that portion ofthe optical fiber element 11 immersed in the etchant J is etched tobecome thinner to form a reduced-diameter portion 14, and simultaneouslythe etching proceeds upwardly into an interface space between the secondresidual coating film 11C-2 constituting the liquid level controllingmeans 40 and the surface of the clad layer until the etching reaches theupper end of the liquid level controlling means. It should be noted thatthere is a slight amount of time lag or time delay for the reach of theetching from the lower end to the upper end of the liquid levelcontrolling means. Due to this time lag, the amount of the etching inradial direction to thin the clad at the lower end of the liquid levelcontrolling means is slightly larger than that at the upper end, so thatthe clad has a second tapered surface portion TP′.

[0091] Once the etching has reached the upper end of the liquid levelcontrolling means 40, the etchant J is further drawn upwardly through anannular gap defined between the liquid level controlling means 40 andthe clad layer to continue with the etching. Thereafter, the etchant Jis still further drawn upwardly along outer periphery of the cladexposed in the second coating film-removed section B due to the surfacetension from the upper end to a certain height M.

[0092] It is thus to be appreciated that a tapered surface portion TP ofaxial length M is formed on the clad layer at the second coatingfilm-removed section B upward from the upper end of the liquid levelcontrolling means 40 by the etchant J as sucked up through the gapbetween the liquid level controlling means 40 and the outer periphery ofthe clad layer. It is further noted that the degree of slant of thesecond tapered surface portion TP′ is relatively small in comparison tothat of the first tapered surface portion TP, so that the second taperedsurface portion can be considered as a part of the reduced-diameterportion 14.

[0093] The location or the lower end of the tapered surface portion TPcan be arbitrarily determined by selecting the axial dimension of theliquid level controlling means 40 (although limited to within the rangeof height of the etchant sucked up by capillary action). The axialdimension M of the tapered surface portion TP is determined by theheight of the etchant rising up above the upper end of the controllingmeans 40, which is in turn determined by the surface tension of theetchant J. In view of these conditions, the upper end of the liquidlevel controlling means 40 is seemed to correspond approximately to thelevel of the etchant J for forming the tapered surface portion TP.Hence, the upper end of the tapered surface portion TP is defined at acertain distance M (see FIGS. 7 and 9) from the upper end of the liquidlevel controlling means 40.

[0094] It is to be noted that FIG. 8 illustrates the optical fiberelement with the reduced-diameter end portion 14T which is obtained fromthe optical fiber element of FIG. 7 by removing the reduced-diameterportion 14 therefrom. It is thus to be appreciated that this embodimentis applicable to an instance in which the location where the taperedsurface portion is to be formed is preliminarily determined.

[0095] In this embodiment, the liquid level controlling means 40 whichis composed of the second coating film-removed section B is observed tobe separated from the outer periphery of the clad layer when the etchinghas reached to the upper end of the liquid level controlling means andto float on the etchant surface by means of the surface tension of theetchant. This fact is quite significant and has never been know from anyprior art. Accordingly, there is no need to employ any support means forsupporting or holding the liquid level controlling means in its properposition.

[0096] Notwithstanding, however, it may be possible to employ anysuitable supporting means, so that such embodiments using the supportingmeans are also involved within this invention.

Fourth Embodiment

[0097]FIG. 10 illustrates another form of the liquid level controllingmeans 40 shown in FIG. 6. As noted hereinbefore, if an attempt is madeto form tapered surface portions on the individual fiber elements 11 ofa tape type optical fiber array 10T comprising a plurality of opticalfiber elements 11 held by a sport 12T with a fine array pitchtherebetween (spacings of 0.25 mm, for example), there would occurundesirable displacement in axial positions of the tapered surfaceportions formed as well as the problem that the axial dimension L of thetapered surface portion will be several times the length of thecorresponding tapered surface portion formed on the single-core fiber,due to the surface tension acting on the individual fiber elements 11overlapping each other as explained with reference to FIGS. 27 and 28.The embodiment of FIG. 10 is directed to an optical fiber end processingmethod capable of resolving such problems.

[0098] In this embodiment as well, each of the optical fiber elements 11exposed from the sport 12T is provided with a first coating film-removedsection A and a second coating film-removed section B, and a liquidlevel controlling means 40 formed by a second residual coating film11C-2 between the first coating film-removed section A and the secondcoating film-removed section B. The liquid level controlling means 40should be formed so as to be uniform in position and axial dimension forall of the optical fiber elements. To this end, apparatus such as laserbeam irradiation apparatus capable of removing a coating film by aiminga laser beam accurately at a predetermined position may preferably beutilized to form the first coating film-removed section A and the secondcoating film-removed section B.

[0099] The end portions of the optical fiber element 11 with the firstcoating film-removed sections A and the second coating film-removedsections B formed thereon are then dipped into an etchant J whileholding the elements in an attitude perpendicular to the liquid surfaceof the etchant J. In doing so, the lower ends of the liquid levelcontrolling means 40 are brought into contact with the liquid surface ofthe etchant J to limit the rising amount of the etchant J. Thislimitation of the rising amount of the etchant J, restrains the heightsof the etchant J rising due to surface tension from the upper ends ofthe respective liquid level controlling means 40 and hence to a constantheight, irrespective of the position of the individual optical fiberelements 11 in the array.

[0100] It will be thus understood that the locations of the taperedsurface portion TP formed by etching are horizontally aligned at aconstant height as shown in FIG. 11. The axial dimensions L of thetapered surface portions TP are also unified throughout the array. Inaddition, it is possible to make the length of the tapered surfaceportions TP approximately equal to that of the corresponding taperedsurface portion formed on a single-core fiber, since the mutualoverlapping of the surface tensions between the individual fiberelements 11 is eliminated and the axial dimensions L of the taperedsurface portions TP are determined by the height M (see FIG. 9) of theetchant J rising from the top of the liquid level controlling means 40.

[0101] Accordingly, for even a multiple-core type optical fiber array,the adoption of the processing method described in this embodimentallows for reducing the length of the tapered surface portions formed atthe forward end thereof, whereby a multiple-core type optical fiberarray 10T provided with highly durable tapered surface portions may beobtained. It is to be noted that in FIG. 11, the original positions ofthe first residual coating films 11C-1 are shown in phantom lines sincethey have already been dropped into the liquid after when thereduced-diameter portions 14 were formed.

[0102] As described before, the second residual coating films arefloated on the liquid surface of the etchant. They may be, however,supported by any other supporting means (not shown).

Fifth Embodiment

[0103]FIGS. 12 and 13 illustrate a fifth embodiment utilizing anotherform of the liquid level controlling means 40. In this embodiment, theliquid level controlling means 40 comprises a flat plate 42 having smallapertures 41 formed therethrough, each having a diameter slightly largerthan the diameter of the corresponding optical fiber element.

[0104] The flat plate 42 may be made of a material such as acrylic resinhaving resistance properties to the etchant J. It is required that thesmall apertures 41 have to have a diameter slightly larger than theouter diameter of the optical fiber element 11 such that the etchant Jmay be drawn up by capillary action through the gaps defined by theinner peripheral walls of the apertures 41 and the outer peripheries ofthe corresponding optical fiber elements 11.

[0105] The liquid level controlling means 40 thus composed by the flatplate 42 with the small apertures 41 may likewise eliminate theoverlapping of surface tensions acting on each other even if a pluralityof optical fiber elements 11 are arrayed with a fine pitch.Consequently, the locations of the individual optical fiber elements 11are made uniform as shown in FIG. 14, as they are determined by theelevation of the upper end of the liquid level controlling means 40. Theaxial dimensions L of the tapered surface portions TP are also madeconstant throughout the array, since they are determined by the height Mof the etchant J rising around the individual optical fiber elements 11.And yet, it is possible to hold the length of the tapered surfaceportions TP down to approximately 0.1 mm which is comparable to that ofthe corresponding tapered surface portion formed on a single-core fiber,hence to provide highly strong tapered surface portions TP.

[0106] While in FIG. 14 the optical fiber elements 11 are illustrated ashaving the reduced-diameter portions 14 remaining, actually thereduced-diameter portions 14 are removed with only the reduced-diameterend portion 14T left below the tapered surface portion TP as shown inFIGS. 5 and 8.

[0107] Further, this embodiment, which utilizes a flat plate 42 havingsmall apertures 41 formed therethrough as a liquid level controllingmeans 40, need not necessarily require that the optical fiber element 11have a coating film 11C. However, such liquid level controlling means 40constituted by a flat plate 42 may equally applied to an optical fiberelement having a coating film 11C for covering the clad layer as shownin FIG. 15. In such case, there need only be a single coatingfilm-removed section A.

Sixth Embodiment

[0108]FIGS. 16 and 17 illustrates modified example of the embodimentsshown in FIGS. 10 and 12. In the embodiment of FIGS. 16 and 17, a liquidK having a specific gravity lower than that of the etchant J isincorporated in the etchant J such that the lighter liquid K floats onthe liquid surface of the etchant J. In the case that the etchant J ishydrogen fluoride, oil may be used as the liquid K. The lighter liquid Kfloating on the liquid surface of the etchant J serves to prevent theetchant J which is climbing up the peripheral surface of the opticalfiber element 11 due to surface tension from being deformed in shape byvibrations, for example.

[0109] More specifically, if vibrations were applied to the etchant Jwhich is adhering and mantling up along the outer peripheral surface ofthe optical fiber element 11 due to surface tension as in theembodiments shown in FIGS. 10 and 12, the etchant J thus attached to theperipheral surface of the optical fiber element 11 may possibly bedeformed in shape. If the shape of the attached etchant J is deformed,the configuration of the resulting tapered surface portion TP is alsodeformed, so that it leads to the disadvantage of reducing themanufacturing yield. With a view to overcoming this drawback, the liquidK having a specific gravity lower than that of the etchant J isincorporated so as to float on the etchant J, whereby the shape intowhich the etchant J mantles up is prevented from being distorted byvibrations, wind pressure or the like. This introduces the advantage ofimproving the production yield.

Seventh Embodiment

[0110]FIG. 18 illustrates yet another embodiment of this invention. Inthis embodiment, an etching-resistant film is deposited on an opticalfiber element 11 devoid of coating film 11C so that theetching-resistant film constitutes a liquid level controlling means 40.

Effects

[0111] As discussed above, according to this invention, the processingmethod involves forming a tapered surface portion TP on a optical fiberelement 11 adjacent to its reduced-diameter portion 14 and subsequentlycutting the reduced-diameter portion 14 in such a manner to leave areduced-diameter end portion 14T. It provides therefore lowering theincidence of flaws such as cracks occurring on the cut faces, andleading to the enhancement of the manufacturing yield in this respect.

[0112] According to another aspect of this invention for application toan optical fiber element 11 having a coating film 11C covering a cladlayer, the processing method involves providing a coating film-removedsection A on the fiber element with a residual coating film 11C lefttoward the forward end thereof and then initiating the etching while thecoating film-removed section A is held in contact with the liquidsurface of the etchant, whereby a desired tapered surface portion TP canbe formed without the need for depositing a resist film 13 (see FIG. 24)for preventing the core from being exposed to the etchant over theforward end of the optical fiber element 11. As a result, this inventionprovides the advantage that a tapered surface portion TP with areduced-diameter portion 14 can be formed by a simple method even on ahighly durable optical fiber element reinforced by a coating film 11C.

[0113] In addition, this invention provides a processing methodcharacterized by a liquid level controlling means 40. The provision ofthis liquid level controlling means 40 makes it possible to determinethe point where the formation of the tapered surface portion TP is to beinitiated. Consequently, this method is well suitable to instances inwhich the location where tapered surface portions are to be formed ispredetermined.

[0114] Moreover, when applied to even an optical fiber array constitutedby a plurality of optical fiber elements 11 held together by a support12T with a fine array pitch, this method utilizing the liquid levelcontrolling means 40 can avoid the phenomenon that the length of thetapered surface portion formed may be elongated depending on theposition of the corresponding optical fiber element 11 in the array dueto the surface tensions acting on the individual fiber elements 11overlapping each other. It will thus be appreciated that for even amultiple-core type optical fiber array 10T, the invention provides theadvantage of forming each of the individual optical fiber elements witha highly durable tapered surface portion. This advantage is extremelygreat in practical use. In addition, when a plurality of single-coreoptical fiber elements 11 are to be formed simultaneously, the provisionof the liquid level controlling means 40 introduces the advantage ofeliminating the mutual overlapping of the surface tensions between theindividual fiber elements 11.

What is claimed is:
 1. A method for processing end portion of an opticalfiber element having a center core and an outer clad surrounding saidcore, comprising the steps of: dipping one end portion of said opticalfiber element into an etchant capable of etching the fiber elementperpendicularly to level surface of said etchant; causing the outer cladof said one end portion of said fiber element immersed in said etchantto be etched into a substantially coaxial reduced-diameter portion whilecausing the outer clad of such a portion of said fiber element that isextended upwardly to a certain height from the level surface of theetchant and that is attached with the etchant which rises upwardly fromthe level surface due to surface tension of the etchant to be etchedinto a conical tapered surface portion which is formed between thereduced-diameter portion and un-etched portion of said fiber element;terminating the etching once said reduced-diameter portion reaches acertain diameter; and cutting said reduced-diameter portion at a pointspaced by a very short distance from the connecting boundary betweensaid tapered surface portion and said reduced-diameter portion towardthe reduced-diameter portion so as to leave a reduced-diameter endportion continuously joining to said tapered surface portion.
 2. Amethod for processing end portion of an optical fiber element having acenter core in the axial center thereof, a cylindrical clad surroundingsaid core and an outer cover coating film surrounding said clad,comprising the steps of: removing said coating film in a partialcylindrical portion thereof having a specified length so as to form acoating film-removed section and a residual coating film section at oneend portion of said optical fiber element; dipping a first part of saidcoating film-removed section and whole part of said residual coatingfilm section disposed at said one end portion of said optical fiberelement into an etchant capable of etching materials of said core andclad of said fiber element perpendicularly to level surface of saidetchant in such a manner that a remaining second part of said coatingfilm-removed section is extending upwardly from the level surface ofsaid etchant to thereby initiate etching process; causing such a portionof the clad as exposed at the first part of the coating film-removedsection of said fiber element and immersed in said etchant to be etchedinto a coaxial reduced-diameter portion while causing such a portion ofthe clad as exposed at the second part of the coating film-removedsection and attached thereto with said etchant which rises to a certainheight above said level surface due to surface tension of the etchant tobe etched into a conical tapered surface portion which is formed betweenthe reduced-diameter portion and un-etched portion of said fiberelement; terminating the etching once said reduced-diameter portionreaches a certain diameter; tapered surface portion has been formed; andcutting said reduced-diameter portion at a point spaced by a very shortdistance from the boundary between said tapered surface portion and saidreduced-diameter portion toward the reduced-diameter portion so as toleave a reduced-diameter end portion continuously joining said taperedsurface portion.
 3. The method according to claim 2, which furthercomprises a step of providing, before the dipping step, a levelcontrolling means for restraining the level surface of said etchant tosaid optical fiber element at a position where said optical fiberelement contacts the level surface of said etchant whereby the axialdimension of said tapered surface portion to be formed on said opticalfiber element is set at a predetermined value.
 4. The method accordingto claim 3 wherein, said level controlling means is constituted by anetching-resistant film formed around the peripheral surface of saidoptical fiber element.
 5. The method according to claim 3 wherein, saidlevel controlling means is constituted by a coating film applied to saidoptical fiber element.
 6. The method according to claim 3 wherein, saidlevel controlling means comprises a flat plate made of etching-resistantmaterial and through-apertures formed through said flat plateperpendicularly to the plane of the flat plate, each of saidthrough-apertures having a diameter slightly larger than the outerdiameter of the corresponding optical fiber element.
 7. The methodaccording to claim 1, which further comprises a step of providing,before the dipping step, a level controlling means for restraining thelevel surface of said etchant to said optical fiber element at aposition where said optical fiber element contacts the level surface ofsaid etchant whereby the axial dimension of said tapered surface portionto be formed on said optical fiber element is set at a predeterminedvalue.
 8. The method according to claim 7 wherein, said levelcontrolling means is constituted by an etching-resistant film formedaround the peripheral surface of said optical fiber element.
 9. Themethod according to claim 7 wherein, said level controlling means isconstituted by a coating film applied to said optical fiber element. 10.The method according to claim 7 wherein, said level controlling meanscomprises a flat plate made of etching-resistant material andthrough-apertures formed through said flat plate perpendicularly to theplane of the flat plate, each of said through-apertures having adiameter slightly larger than the outer diameter of the correspondingoptical fiber element.
 11. The method according to any one of precedingclaims 1 through 10 wherein, a liquid having a specific gravity lowerthan that of said etchant is mixed into said etchant.
 12. The methodaccording to claim 11, wherein a plurality of said optical fiberelements held in parallel to each other by a single common coveringmember to thereby form an optical fiber array, are subjected toprocessing.
 13. The method according to any one of claims 1 through 10,wherein a plurality of said optical fiber elements held in parallel toeach other by a single common covering member to thereby form an opticalfiber array, are subjected to processing.
 14. An optical fibercomprising an optical fiber element having a center core and a outerclad surrounding said core, characterized by having at one end thereof aconical tapered surface portion with a reduced-diameter end portion. 15.The optical fiber according to claim 14, wherein said reduced-diameterportion has a diameter larger than that of the core of said opticalfiber element.
 16. The optical fiber according to any one of claims 14or 15, wherein said reduced-diameter end portion has a length no morethan its diameter.
 17. A method for processing end portion of opticalfiber element having a center core and an outer clad surrounding saidcore, comprising the steps of: dipping one end portion by a certainlength of said optical fiber element into an etchant capable of etchingcore and clad materials perpendicularly to level surface of said etchantin such a manner that outer periphery of said clad is exposed to theetchant; time controlling so as to cause such a portion of the cladlocated at said one end portion as immersed in said etchant to be etchedinto a reduced-diameter portion of a substantially coaxial shape whileto cause such a portion of the clad as extended upwardly to a certainheight from a level surface of the etchant where said etchant isattached and rises upwardly from the level surface due to surfacetension of the etchant to be etched into a conical tapered surfaceportion wherein lower and upper ends of the tapered surface portion arecontinuously connected to the reduced-diameter portion and outerperiphery of the un-etched clad, respectively; terminating the timecontrolling once said reduced-diameter portion reaches a certaindiameter; and cutting said reduced-diameter portion so that areduced-diameter end portion is obtained which is continuously joiningto said tapered surface portion.